So far, I've come up with one reason why: He has the same birthday as I do. We were both born on August 20 (different years, of course).
Anyway, I came across that interesting bit of trivia while reading through a story on Paul's presidental campaign, on the SF Chronicle's website. Interesting piece.
Interestingly, if elected, Paul would be the 2nd U.S. president to share my birthday. Good ole Benjamin Harrison was born August 20, 1833. More on presidential birthdays here.